1. Field of the Invention
The present invention relates to the preparation of catalysts employed in hydroformylating olefins in the presence of carbon monoxide and hydrogen at elevated temperatures and pressures in order to produce aldehydes which are converted by hydrogenation to alcohols. More particularly, it pertains to a novel process for the continuous synthesis of oxo catalysts by employing an extraction mechanism at a much reduced cost.
The oxo process is well known and involves the preparation of oxygenated organic compounds by the reaction of carbon monoxide and hydrogen (synthesis gas) with carbon compounds containing olefinic linkages in the presence of a carbonylation catalyst at hydroformylation conditions which include synthesis gas pressures of 1500 to 4500 psig and temperatures in the range of 150.degree.-450.degree. F.
This carbonylation reaction provides a particularly attractive method for preparing valuable primary alcohols which find large markets, particularly as intermediates for plasticizers, detergents and solvents. Amenable to the reaction are long and short chained olefinic compounds, depending upon the type alcohols desired. Not only olefins, but most organic compounds possessing at least one non-aromatic carbon-carbon double bond may be reacted by this method. Thus, straight and branch-chained olefins and diolefins such as propylene, butylene, pentene, hexene, heptene, butadiene, pentadiene, styrene, olefin polymers such as di- and triisobutylene and hexene and heptene dimers, polypropylene, olefinic fractions from the hydrocarbon synthesis process, thermal or catalytic cracking operations, and other sources of hydrocarbon fractions containing olefins may be used as starting material, depending upon the nature of the final product desired. C.sub.5 to C.sub.13 olefins are commonly used olefin starting materials.
2. Description of the Prior Art
Typically, in a cobalt-catalyzed oxo process, the catalyst material is fed into the oxonation reactor in the form of an oil-soluble soap, e.g., cobalt oleate. Such a cobalt soap is then converted in situ to cobalt tetracarbonyl hydride or cobalt hydrocarbonyl, which is presumed to be the catalytically active species. After the oxonation, said cobalt hydrocarbonyl, HCo(CO).sub.4, is normally separated from the oxo product by way of the following demetalling process: ##EQU1## This conversion of oil-soluble/water-insoluble cobalt hydrocarbonyl to water-soluble/oil-insoluble cobalt acetate makes it possible to separate the cobalt catalyst from the oxo product stream and recover the cobalt as cobaltous ion, Co.sup.+2. The aqueous layer which contains the cobaltous compound, e.g., cobalt acetate, is called demetalling water or, briefly, demet water.
In general, this demet water is neutralized with caustic and thereafter reacted with a high molecular weight carboxylic acid, e.g., oleic acid to form an oil-soluble cobalt soap, e.g., cobalt oleate which is extracted by olefin, as represented by the following equations: ##EQU2## The cobalt soap so formed is further diluted with the olefinic feed before it is fed to the oxonation reactor and waste water is sent to disposal.
There are a number of deficiencies associated with this conventional catalyst synthesis cycle. First, it has been discovered that the cobalt hydroxide formed in Equation 2 tends to cause the formation of emulsions, which necessitates the use of a batch reactor with stirring at a critical rate in the synthesis of the cobalt soap. Secondly, in order to minimize the emulsion or precipitation of the cobalt hydroxide, it is necessary to maintain the reaction medium within a narrow, neutral range, e.g., pH=6.5-7.5, with constant and vigorous stirring. If the pH of the soap synthesis mixture is lower than the neutral range, i.e., acidic, a lesser amount of cobalt soap would be recovered in Equation 3; and if the pH goes higher, then a higher level of emulsion or precipitation of cobalt would result. In either event, the system is highly susceptible of sizable cobalt loss and severe pollution problems. Thirdly, in this conventional catalyst cycle, the high cost high molecular weight carboxylic acids, e.g., oleic acid, employed as the catalyst carrier, are normally discarded after a single cycle. This limited usage of carrier acid coupled with the use of acetic acid and caustic on a once-through basis makes the conventional method economically disadvantageous.
Attempts have been made to ameliorate the above-mentioned deficiencies. In U.S. Pat. No. 3,234,146 to Null et al, the crude oxo product is demetalled by treating it with a mineral acid such as nitric; the oxo product is then saponified and the alkali soap is extracted with water into an aqueous phase. The aqueous inorganic salts of cobalt and manganese are caused to react with the aqueous alkaline soap in the presence of a heavy alcohol to form the Co and Mn soaps. When operating in this manner, the patentees have found that there is a restrictive requirement in that the synthesis of the cobalt-manganese soap must be carried out in a well stirred batch reactor at a pH in the range of from 7 to 9. Accordingly, this process does not provide the continuous synthesis of the catalyst soap needed to debottle-neck the entire oxo process. In addition, it is still subject to close pH control of the catalyst synthesis system.